1. Field of the Invention
The present invention relates to a device having a communication function, an automatic transmitter adjusting method, a system and a program applicable to a high-speed serial transmission interface or the like performing two-way data transmission of the order of giga-bit per second. More particularly, the invention relates to a device having a communication function, an automatic transmitter adjusting method, a system and a program capable of adjusting properties of a transmitter such as output amplitude and emphasis to optimum values on the basis of transmission of sample data.
2. Description of the Related Art
As input/output interfaces of personal computers or embedded devices, for example, PCI buses had conventionally been used. More recently, however, along with the tendency toward a higher processor operating frequency, high-speed serial interfaces of giga bit/second (Gbps) have been industrialized, and are becoming more and more popular.
Such a high-speed serial interface uses a differential transmission line comprising two signal lines having opposite polarities for transmission of bits. More specifically, the differential output of a transmitter (driver) of a device is connected to two signal lines, and the two signal lines are connected to the differential input of the receiver of the destination device. Since the characteristic impedance of the transmission line is regulated, for example, to 50Ω, the two signal lines terminates with a resistance of, for example, 50Ω at each device.
The adoption of such a differential transmission line improves the resistance to so-called common mode noise which acts simultaneously on two signal lines, facilitates high-speed operation by reducing the signal amplitude on the receiving side, and inhibits power loss caused by terminal resistance.
As a differential transmission line operates in a single direction, two-way transmission is ensured by using four signal lines. These four signal lines for carrying out two-way transmission are referred to as a lane. For example, in PCI Express known as a high-speed serial interface, the maximum data transfer rate per direction is 2.5 G bits/second (2.5 Gps). The actual maximum data transfer rate is however 2.0 G bits/second corresponding to 80% thereof, and for a lane, it becomes 4.0 G bits/second.
However, in such a conventional high-speed serial interface, permitting high-speed transmission of the giga-bit order per second, it is necessary to evaluate and determine optimum set values of output amplitude and emphasis of the transmitter for each device through a real-machine test, and determination of optimum values requires much time and labor.
That is, a real-machine evaluation is based on an operation comprising the steps of high-speed-serial-transmitting sample data from a transmitter by use of a signal generator, displaying an eye diagram by entering the sample data into a measuring instrument, and finding optimum values by changing the output amplitude and emphasis of the transmitter so that the amplitude is appropriate and the jitter becomes minimum from the eye diagram. For example, display of an eye diagram of a run of measurement requires transmission of sample data for 20 to 30 seconds, and this should be done for all the states of which the setting can be changed of the output amplitude and emphasis. Finding optimum values of output amplitude and emphasis thus becomes a very troublesome operation requiring much time and labor.
In the case of multiple lanes, furthermore, determining an optimum value for each lane is difficult since it takes too much time and labor. It is therefore inevitable to use a method of making a confirmation for a typical lane and adopting similar transmitting conditions for the other lanes. This causes a problem in that adjustment of high-speed serial interfaces is not always necessary and sufficient.
It is an object of the present invention to provide a device having a communication function, an automatic transmitter adjusting method, a system and a program in which optimum values of output amplitude and emphasis of the transmitter through automatic adjustment without requiring an artificial real-machine evaluation.